In recent years, an emission regulation has been strengthened and a minimum injection quantity (Qmin) of fuel by a fuel injector has been required to be reduced. There has been known a technique to use a partial lift range (range in which the valve body is brought into a partial lift state before the valve body reaching a full lift position) of a needle (valve body) of the fuel injector in order to reduce the minimum injection quantity (Qmin). In this range, the minimum injection quantity (Qmin) is greatly affected by a difference in an injection characteristic caused by an individual difference of the fuel injector. For this reason, the injection characteristic at the time of the partial lift injection is learned and an injection command value is corrected on the basis of a learned result.
For example, there is proposed a technique that compares a driving voltage UM of a solenoid with a reference voltage UR generated by filtering the driving voltage UM by a low pass filter to thereby detect an armature position of the solenoid on the basis of an intersection of them.
As shown in Patent Literature 1, the fuel injector is driven in such a way as to inject a request quantity of fuel. For this reason, even if the injection characteristic at the time of the partial injection is tried to be learned, a state in which the partial lift injection is performed results in being limited.